Saudi-led airstrikes killed at least 26 people at a police facility in Yemen's capital overnight, adding to a death toll of nearly 6,000 people since Riyadh began its military campaign against the Houthi militia that controls Sana'a.

The attack on police headquarters wounded dozens more people, many of them police officers. Rescue efforts were under way for survivors trapped under the debris of the building.

On Sunday, a Saudi coalition airstrike killed an independent reporter for Voice of America and the humanitarian news agency, IRIN. Almigdad Mojalli was the sixth journalist killed in Yemen since January 2015.

"Almigdad Mojalli was a committed and talented journalist who made the ultimate sacrifice to report on the difficult, but important, stories coming out of Yemen," said John Lansing, the director of the Broadcasting Board of Governors - the parent organization of the Voice of America. "He dedicated his life to reporting on humanitarian crises, and we extend our condolences to his family," Lansing said.

The U.S. State Department also expressed condolences to Mojalli's family and said it is still in the process of gathering information about the circumstances of his death.

Since October, Mojalli had been reporting for VOA on the human impact of the war and the economic crisis in Yemen. He was in an area outside of rebel-held Sana'a on Sunday morning when he was killed in the Saudi-led coalition airstrike.

Houthi rebels overran the capital in late 2014, triggering the resignation of President Abd Rabbu Mansour Hadi in January 2015 and subsequent exile to Riyadh.

Leading a regional coalition, Saudi Arabia has carried out an air campaign against the Houthis since March.